In recent years, among internal combustion engines mounted in automotive vehicles, an increasing number have employed variable valve timing devices for varying the valve timing of intake valves and exhaust valves with the object of increasing output, reducing fuel consumption, and lowering exhaust emissions. Most variable valve timing devices in use at present change the valve timing of intake valves and/or exhaust valves driven to open and close by a camshaft by driving a phase-varying mechanism with hydraulic pressure to vary the rotation phase of the camshaft with respect to a crankshaft. However, in a hydraulically driven variable valve timing device like this there is the shortcoming that in cold conditions and on starting of the engine the hydraulic pressure is insufficient, the responsiveness of hydraulic control falls, and the accuracy of valve timing control falls.
In this connection, as disclosed for example in JP-A-6-213021, motor-driven variable valve timing devices have been developed, in which a phase-varying mechanism is driven with drive power from a motor to vary the rotation phase of a camshaft with respect to a crankshaft and thereby vary a valve timing.
However, in this motor-driven variable valve timing device of related art, because the construction is such that the motor as a whole rotates integrally with a pulley rotationally driven by the crankshaft, there is the shortcoming that the inertial weight of the rotating system of the variable valve timing device is heavy and the durability of the variable valve timing device is poor. Furthermore, a sliding contact arrangement using brushes or the like has to be used to connect the rotating motor with external electrical wiring, and this also constitutes a cause of reduced durability. Also, motor-driven variable valve timing devices of related art have had the shortcoming that their overall construction is complex and they are high in cost.
The present invention was made in view of these circumstances, and an object of the invention is to provide a variable valve timing control device of an internal combustion engine with which while fulfilling the requirements of increased durability and reduced cost of a variable valve timing device it is possible to control a valve timing by motor drive and it is possible to raise the accuracy of valve timing control.